Skeleton farm [Can't hit legs]

So yeah I got this little bug here, I created some exp/item farms, and I have to be able to kill them when hitting the skeletons feet, unfortunately this doesn't work and you have to get shot to kill them
(Also great loss of exp since the skeletons will shoot eachother).

I don't know if this is a 1.1 bug for SMP, still, or if it just is something done throughout the server files?